Erythropoietin and its Non-Hematopoietic Activities
Erythropoietin (EPO), a 165 amino acid glycoprotein hormone, was identified initially as a hematopoietic growth factor and has been used extensively for the treatment of anemia in humans. Whole molecule EPO received considerable attention recently because it may have broad neuroprotective capabilities following CNS injury [Brines, M. L., et al., Proc Natl Acad Sci USA, 97: 10526-31 (2000); Siren, A. L. and Ehrenreich, H., Eur Arch Psychiatry Clin Neurosci, 251: 179-84 (2001); Buemi, M., et al., J. Neuropathol Exp Neurol, 62: 228-36 (2003); Li, W., et al., Ann Neurol, 56: 767-77 (2004); Sakanaka, M., et al., Proc Natl Acad Sci USA, 95: 4635-40 (1998)]. Therapeutic effects of exogenously administered EPO on several diverse forms of neurologic injury, including occlusive cerebral vascular disease, acute brain trauma, epilepsy, and an autoimmune model of demyelinating disease, experimental autoimmune encephalomyelitis (EAE), have been tested and the degree of neurologic impairment was significantly reduced [(Brines, M. L. et al., Proc Natl Acad Sci USA, 97: 10526-31 (2000); Li, W. et al., Ann Neurol, 56: 767-77 (2004); Tsai, P. T., et al., J Neurosci, 26: 1269-74 (2006); Buemi, M., et al., Clin Sci (Lond), 103: 275-82 (2002)]. However, long-term EPO therapy remains significantly limited in non-anemic patients with neurological injury because EPO treatment may overly stimulate erythropoiesis. To overcome this concern, EPO therapy would have to be limited to very short term use. Other EPO molecular preparations, such as an asialo-form of EPO, carbamylated EPO (CEPO), or certain EPO mutants, have been shown to be neuroprotective in animals following experimental traumatic spinal cord injury or acute stroke without provoking an increase in red cell mass [Erbayraktar, S., et al., Proc Natl Acad Sci USA, 100: 6741-46 (2003); Leist, M., et al., Science, 305: 239-42 (2004); Mun, K. C. and Golper, T. A. Blood Purif, 18: 13-17 (2000); Brines, M., et al., Proc Natl Acad Sci USA, 101: 14907-12 (2004). A short 17 amino acid EPO-derived linear peptide also was reported to have neuroprotective effects in cell culture, but its in vivo biologic effects were not certain [Campana, W. M., et al., Int'l J Mol Med, 1: 235-41 (1998). Taken all together, the evidence suggests that specific functional and structural domains may co-exist within the full 165 amino acid EPO molecule.
The hematopoietic effect of EPO is mediated by binding and inducing dimerization of two molecules of the EPO receptor (EpoR) on the cell surface [Watowich, S. S., et al., Mol Cell Biol, 14: 3535-49 (1994)]. The EpoR belongs to a cytokine receptor superfamily that is also related to the cytokines granulocyte colony-stimulating factor (G-CSF), granulocyte macrophage colony-stimulating factor (GM-CSF), interleukins 2-7 and ciliary neurotrophic factor (CNTF). The signaling pathway involves the autophosphorylation and activation of the Janus family protein tyrosine kinase, JAK-2, which further activates additional signaling proteins including STAT5, Ras-mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K). Studies on structure activity relationships of EPO have identified regions and amino acids essential for binding to the erythropoietin receptor (EpoR) [Livnah, O., et al., Science, 273: 464-71 (1996); Wrighton, N. C., et al., Science, 273: 458-64 (1996); Wen, D., J Biol Chem, 269: 22839-46 (1994)]. Studies in which recombinant EPO and EPO mutants have been tested for their biological effects in a variety of animal models have suggested that the neuroprotection mediated by EPO might not occur through a conventional interaction between EPO and classic EpoR. The common β receptor (βcR) or CD131, which is also an important component for other ligands including IL-3, IL-5 and GM-CSF, has been proposed to be a key subunit associated with the EpoR that is responsible for EPO mediated non-hematopoietic effects. Additional unknown receptor(s) also may play critical roles in the non-hematopoietic effects induced by chemically modified or mutant EPO. Based on the belief that there are at least two distinct functional peptide domains co-existing within the whole EPO molecule and that sequences and/or structures within the EPO-derived peptides will dictate their biological functions, small EPO-derived peptides with different biological functions having neuroprotective and immunomodulatory activity have been identified and characterized herein.
EAE Animal Model and Multiple Sclerosis
Multiple sclerosis (MS) a disorder of unknown cause, is defined clinically by characteristic symptoms, signs and progression, and is defined pathologically by scattered areas of inflammation and demyelination affecting the brain, optic nerves and spinal cord white matter. It is widely believed that the pathogenesis of MS involves an immune-mediated inflammatory demyelinating process.
Experimental autoimmune encephalomyelitis (EAE) is a central nervous system inflammatory demyelinating disease involving acute injury to the brain and spinal cord white matter. This animal model has been used widely by many investigators to study disease pathogenesis and to explore new therapies for its human counterpart, multiple sclerosis (MS). Pathogenesis of both MS and EAE is believed to involve (1) activation of myelin reactive T cells; (2) upregulated expression of chemokines and adhesion molecules; (3) focal T cells and macrophage infiltration into the CNS white matter; and (4) demyelination and axonal injury and loss of neurological function [Trapp., B. et al., J Neuroimmunol, 98: 49-56 (1999)]. In both EAE and MS, activated T-lymphocytes specific for self-antigens present in myelin are linked to CNS inflammation and to the breakdown of the blood brain barrier to peripheral blood leukocytes and plasma proteins; this is predominantly restricted to myelin rich white matter area of the CNS [Bettelli, E., et al., J Exp Med, 197: 1073-81 (2003); Crawford, M. P., et al., Blood 103(11): 4222-31 (2004); Abdul-Majid, K. B., et al., J Neuroimmunol, 141: 10-19 (2003); Battistini, L., et al., Blood, 101: 4775-82 (2003).
EAE can be induced experimentally in genetically susceptible animals, such as mice, by immunization with immunodominant peptides from myelin proteins, such as myelin basic protein (MBP), proteolipid protein (PLP), and myelin oligodendrocytes glycoprotein (MOG), emulsified in complete Freund's adjuvant followed by injection of pertussis toxin as an additional adjuvant for certain mouse strains [Li, W., et al., Ann Neurol, 56: 767-77 (2004). Disease development is variable from strain to strain. For example, in SJL/J mice, PLP or MBP induces a relapsing-remitting progression, whereas C57BL/6 mice immunized with MOG often develop a chronic form of disease.
A library of stabilized isolated EPO-derived peptides comprising about 7 to about 25 amino acids in length has been created and tested in vitro and in vivo for therapeutic efficacy. It has been shown that these short EPO-derived peptides are highly protective in mouse models of EAE, acute stroke, acute spinal cord and brain injury as well as arthritis by reversing and/or reducing manifestations of the associated disease. This protection is maintained during long term observation in EAE mice and was not associated with hematological side effects. These short peptides protect against tissue damage by modulating the immune-mediated inflammatory network, i.e. by reducing major histocompatibilty complex (MHC) class I and class II over-expression; by reducing inflammatory cytokines; and by suppressing antigen-specific T cell function in peripheral lymphoid tissue and brain tissue as well as in in vitro tissue culture assays. The peptide domain that is crucial for immunomodulating/anti-inflammation functions as well as a small peptide ring that plays an important role in maintaining the stability, without hampering biologic efficacy, of these small peptides have been identified. Moreover, addition of a small bicyclic compound, such as d-biotin, to the N- or C-terminal of linear cytokine-derived peptides, including, but not limited to, short EPO linear peptides, the stability of these peptides is increased without hampering their biologic activity. These newly developed small peptides hold immense potential for direct clinical application in treatment of central and peripheral nervous system diseases associated with injury including demyelinating diseases, traumatic injury and stroke. Since the beneficial effect of these peptides is not limited to neural tissue organs, they are broadly useful in the treatment of inflammatory/immune injury to non-neural organs of the body.